The present invention relates to an ink jet printer employing a cleaning technique for preventing the nozzles of a print head from being clogged, particularly in an ink jet printer of the type which uses high viscosity ink which hardens easily so as to improve print quality.
In a known ink jet printer, a print head includes a plural number of combinations each including a pressure generating chamber, a nozzle communicating with the pressure generating chamber, and a pressure generating element for varying the pressure within the pressure generating chamber. Print data signals drive the pressure generating elements to cause the discharge of a stream of ink droplets through the nozzles. An image is formed by the ink droplets discharged. This type of ink jet printer requires a smaller number of movable parts than a wire impact type printer. In this respect, the former is superior to the latter. Accordingly, the former printer has advantages of generation of less noise and reduction of the size and cost. However, the former is inferior to the latter for the reason that since ink in liquid form is used to print images on a print paper, some types of print paper blot easily, deteriorating print quality.
U.S. Pat. No. 4,538,156 succeeds in solving the blotting problem. As disclosed therein, an intermediate recording medium is provided in the form of a drum or a belt. Ink droplets from the print head are received by the intermediate recording medium. After ink solvent is volatilized to some extent, the ink image formed on the recording medium is transferred to the print paper. With this arrangement, the paper does not blot, regardless of its type, and good print quality is secured.
However, the printer of the above-mentioned patent must use ink of higher viscosity than a printer which projects streams of ink droplets toward the print paper directly in order to secure reliable transfer of the ink image from the intermediate recording medium to the print paper. Ink mist generated when ink is jetted through nozzle openings and ink spray bouncing from the intermediate recording medium collect on and adhere to the front face of the nozzle and form stiff films thereon. The thus-formed films can cause the jets of ink droplets to deviate from the intended course, leading to deterioration of print quality. To avoid this, the ink films must be removed at appropriate intervals of time.
The ink jet printer of the type in which ink is directly jetted toward the print paper suffers from the same problem. To cope with this, many types of cleaning devices have been proposed to remove ink adhering to the front face of the nozzle plates. However, in general these cleaning devices have been found to insufficiently remove the ink which contains compositions such as certain emulsions or sugars added thereto so as to increase the viscosity of ink and make it easy to form ink films of a type which attains improved print quality.